1. Field of the Invention
The present invention relates generally to drywall lifters and more specifically it relates to a mobile hoist system for reliably preventing the application of an overloading input force or an overloading weight force from an elevated load.
2. Description of the Related Art
Any discussion of the related art throughout the specification should in no way be considered as an admission that such related art is widely known or forms part of common general knowledge in the field.
Drywall lifters have been in use for years. A conventional drywall lifter is comprised of a telescoping structure attached to a base, an upper support attached to an upper portion of the telescoping structure and a drive unit mechanically connected to the telescoping structure to selectively lift and lower the telescoping structure. The drive unit may be manual or hydraulic. A drywall panel is positioned upon the upper support and is thereby raised to a desired position on a ceiling for securing by workers with conventional fasteners and then removed after fastening. U.S. Pat. No. 5,586,619 (hydraulic lifter) to Roland Young, U.S. Pat. No. 5,368,429 (manual lifter) to Roland Young and U.S. Pat. No. 3,828,942 (manual lifter) illustrate examples of conventional drywall lifters.
While some drywall lifters utilize a slip clutch on the input force side, they utilize a one way brake on the weight force side which limits the slip clutch to only usage one way from the input force side as illustrated in FIG. 1 of the drawings. Hence, if an overload weight force is applied, the one way brake is prone to breakage after a weight level has been reached which can result in damage to the drywall lifter and possibly personal injury.
Hence, there is a need for a drywall lifter that prevents an overload failure on the weight force side of the drywall lifter to prevent damage to the drywall lifter and to prevent personal injury.